An experimental investigation of the partitioning of iron isotopes between silicate melt and spinel as a function of oxygen fugacity

硅酸盐熔体和尖晶石之间铁同位素分配随氧逸度变化的实验研究

• 批准号: NE/D007801/1
• 负责人: Andrew Berry
• 金额: $ 4.12万
• 依托单位: Imperial College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2006
• 资助国家: 英国
• 起止时间: 2006 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FD007801%2F1
• 关键词: experimental; investigation; partitioning; iron; isotopes

Iron (Fe) is the most common element in the Earth's mantle that occurs in more than one oxidation state (as Fe2+ and Fe3+). It also occurs as four isotopes (54Fe, 56Fe, 57Fe and 58Fe). It has only recently been discovered that these isotopes may be fractionated during high temperature mantle processes such as partial melting. In particular mantle spinels exhibit a correlation between isotope fractionation and oxygen fugacity, which controls the relative amounts of Fe3+ and Fe2+. The importance of oxygen fugacity in controlling this fractionation relative to other process such as mantle metasomatism is unclear. There is currently no experimental evidence to independently establish the effect of variable Fe3+/Fe2+ on the fractionation of Fe isotopes in spinel at magmatic temperatures. In this work we propose to crystallise a series of spinels from a melt as a function of oxygen fugacity. The samples will be prepared by equilibrating a melt, with spinel on the liquidus, at atmospheric pressure in a controlled gas environment. After quenching, the spinel and melt will be separated and analysed by Mössbauer spectroscopy to determine Fe3+/Fe2+, and with a high-resolution multi-collector inductively coupled plasma mass spectrometer to determine the Fe isotopic ratios. This will allow oxygen fugacity, the Fe3+/Fe2+ ratio, and isotope fractionation to be directly correlated. Experiments of this type are essential if variations in Fe isotopic measurements of natural samples are to be correctly interpreted, thus providing a new tool for tracking mantle processes. This project applies techniques commonly used in the area of experimental petrology to an emerging area of isotope geochemistry.

铁（Fe）是地球地幔中最常见的元素，以一种以上的氧化态（如Fe 2+和Fe 3+）存在。它也以四种同位素（54 Fe，56 Fe，57 Fe和58 Fe）存在。直到最近才发现，这些同位素可能在高温地幔过程（如部分熔融）中发生分馏。特别是地幔尖晶石表现出同位素分馏和氧逸度之间的相关性，这控制了Fe 3+和Fe 2+的相对量。相对于其他过程，如地幔交代作用，氧逸度在控制这种分馏中的重要性尚不清楚。目前还没有实验证据来独立地确定可变的Fe 3 +/Fe 2+在尖晶石中的Fe同位素在岩浆温度下的分馏的效果。在这项工作中，我们提出了一系列的尖晶石从熔体作为氧逸度的函数结晶。样品将通过在受控气体环境中在大气压下平衡熔体来制备，其中尖晶石在液相线上。淬火后，尖晶石和熔体将被分离，并通过穆斯堡尔光谱法进行分析，以确定Fe 3 +/Fe 2+，并使用高分辨率多接收器电感耦合等离子体质谱仪来确定Fe同位素比率。这将允许氧逸度，Fe 3 +/Fe 2+比，和同位素分馏直接相关。这种类型的实验是必不可少的，如果要正确解释天然样品的Fe同位素测量的变化，从而提供了一个新的工具，跟踪地幔过程。该项目将实验岩石学领域常用的技术应用于同位素地球化学的新兴领域。